The present invention relates to a vacuum pump determining a rotor temperature using the Curie temperature of a magnetic body.
In a turbo-molecular pump, an aluminum alloy is generally used as the rotor material. In the aluminum alloy, an allowable creep deformation temperature is relatively low (approximately 120° C.˜140° C.), so that when a pump is operated, it is required to be constantly monitored in order that the temperature of the rotor may be kept below the allowable temperature. Accordingly, a non-contact method for detecting the temperature of the rotor by using the phenomenon that the magnetic permeability of a ferromagnetic body greatly changes at the Curie temperature, is also known (for example, refer to Japanese Patent Publication No. H7-5051). In this conventional method, a ring-shaped ferromagnetic body is installed around a rotor, and the change of the magnetic permeability of the ferromagnetic body in Curie temperature is detected by an inductance detection coil.
However, if the carrier signal frequency applied to the coil is low, the sensor signal can be easily distorted by the rapid change of the magnetic permeability or the gap between the magnetic body and sensor. In order to prevent the above-mentioned distortion, generally, the carrier signal is required to be set at a high frequency. On the other hand, in order to meet a sampling theorem at the time of digitalization, if the carrier signal frequency is high, the sampling frequency is also required to be high. However, if the sampling frequency is high, a DSP or CPU with a low frequency operation may not be able to handle it, so that an expensive high-frequency-compliant DSP or CPU has to be used. As a result, the cost increases.
The present invention has been made to obviate the problems in the conventional vacuum pump.
Further objects and advantages of the invention will be apparent from the following description of the invention.